1. Field of the Invention
The present invention relates to a method and to an arrangement for transmitting characters from a transmitting station to a receiving station in which the characters are emitted by a data source and are ciphered in a transmitting station and the ciphered characters are deciphered in a receiving station and output to a data sink and wherein the ciphered characters have a first plurality m of binary characters. More specifically, in the transmitting station a respective second plurality n of binary characters of successive, ciphered characters is provided with a prescribed plurality of binary fill characters, the number n being smaller than the number m of binary characters.
2. Description of the Prior Art
When characters encoded in accordance with an internationally-predetermined code are ciphered in a transmitting station, are transmitted to a receiving station, and are deciphered in the receiving station, binary combinations can occur as ciphered characters which denote control characters in accordance with the code of the unciphered characters. These control characters are, for example, the characters for "carriage return", "new line", "letters", "numerals", "space" or the character which only contains the binary characters zero. When the ciphered characters are transmitted and deciphered in the receiving station, then the randomly-occurring control characters do not have a disruptive effect because the originally-existing characters reoccur in the course of the deciphering instead of the randomly-occurring control characters. In some instances, however, it is desirable to record the ciphered characters, for example, to output the same with the assistance of a printer. This, however, is not possible because the printer responds to the randomly-occurring control characters. When, for example, a ciphered character occurs which corresponds to the control character "carriage return", then the printer recognizes the control character and the triggered carriage return is undertaken at a point in the text which is generally entirely unsuitable.
Declared sequences of alphanumerical characters are likewise true as control characters in some procedures for the transmission of characters. This is particularly the case when the characters are transmitted either unciphered, or ciphered, over a transmission link and sequences of characters are then transmitted as control characters, the occurrences of the sequences in a normal text being extremely improbable. Such control characters are formed, for example, by four successive letters M or S. The occurrence of such control characters in a ciphered text is likewise undesired since, for example, a switching center located in the transmission link prematurely disconnects the connection, or initiates other undesired control operations.
It is known from the German Letters Patent No. 25 53 897, fully incorporated herein by this reference, to only cipher the alphanumerical characters and to transmit the control characters unciphered to the receiving station. The occurrence of individual, ciphered characters whose bit combinations represent a control character is thereby advantageously prevented by a corresponding reduction in the supply of ciphered characters. By so doing, it is guaranteed that the ciphered text is represented in accordance with the input text given the operating mode initially mentioned in which the ciphered text is printed at the receiving station. The occurrence of the last-cited control characters, consisting of a plurality of letters, within the ciphered characters, however, cannot be prevented with this known method.